The overall aim is to define quantitative and temporal relationships between secretion of selected hypothalamic hormones and secretion of prolactin and luteinizing hormone. The approach will involve simultaneous monitoring of hypothalamic and anterior pituitary hormone secretion. Specific aims are: (1) To test the hypothesis that testicular hormones, particularly testosterone, elevate LHRH while depressing LH. We will do this by monitoring LHRH in perfusates of the stalk median eminence (SME) collected by push-pull cannulae (PPC) and LH in blood of conscious rams, wethers, and testosterone-treated wethers; (2) To test the hypothesis that gonadal steroids have divergent temporal effects on LH and LHRH secretion. We will do this by monitoring changes in LHRH concentrations in SME perfusates collected by PPC, and LH in blood of intact ewes during three stages of the estrous cycle; (3) To test the hypothesis that photoperiod-induced changes in prolactin secretion are mediated primarily by changes in secretion of dopamine (DA). We will do this by monitoring changes in concentrations of DA, DA metabolites, and vasoactive intestinal peptide (VIP) in PPC perfusates of the SME of conscious ewes exposed to long and short photoperiods. Prolactin will be measured in venous blood; (4) To test the hypothesis that morphine elevates prolactin secretion primarily by reducing DA secretion. We will monitor DA, DA metabolites, TRH, and VIP concentrations in PPC perfusates and prolactin in blood of conscious ewes treated with saline solution or morphine; (5) To test the hypothesis that suckling induces prolactin release by reducing DA secretion and elevating TRH or VIP secretion. We will monitor DA, DA metabolites, TRH and VIP concentrations in PPC perfusates and prolactin in blood of conscious ewes prior to, during, and after suckling; and (6) To test the hypothesis that prolactin release induced by elevated ambient temperature is mediated primarily by increased secretion of TRH. We will monitor DA, DA metabolites, TRH, and VIP concentrations in PPC perfusates and prolactin in blood of conscious ewes before, during, and after exposure to elevated ambient temperatures.